Electric spark discharge machining abnormal discharge current detection method and device

Abstract

The invention relates to an abnormal discharge current detection method and device for electric spark discharge machining, and is applied to the technical field of discharge machining. A direct current-direct current power supply module is adopted as a current detection core element, has a stable voltage output characteristic and is sensitive to current fluctuation response, and a traditional Hall sensor is replaced; the problem of high-precision detection of small current in a strong electromagnetic interference environment is successfully solved; on the basis of current rising edge characteristic differences of abnormal discharge and normal discharge, two key time points are selected for voltage comparison, abnormal states such as excessive arc, arc, short circuit and micro open circuit can be accurately distinguished, and missed judgment and misjudgment are avoided; a reference value lookup table corresponding to different peak currents is established through experimental calibration to adapt to various medium and finish machining parameter scenes; and the detection branch adopts the design of an isolation diode and a current-limiting resistor, and is matched with pulse-type intermittent measurement of a controlled switch tube, so that shunting interference on a main discharge loop is avoided, and the stability of the processing process is ensured.

Description

Technical Field

[0001] This invention relates to the field of electrical discharge machining technology, specifically to a method and device for detecting abnormal discharge current in electrical discharge machining. Background Technology

[0002] In the high-end mold field of electrical discharge machining, especially for integrated circuit packaging molds, stringent requirements are placed on the surface quality of the machined parts. The surface roughness must be uniform and consistent, and pinhole defects are absolutely unacceptable. These pinhole defects mainly arise from abnormal discharge, accidental malfunction of the discharge gap, or excessive impurities in the electrical discharge machining fluid. The most significant cause is excessive arcing and abnormal discharge induced by the arc.

[0003] Engineering practice in electrical discharge machining (EDM) shows that the combination of extremely short pulses (below 10 microseconds) and high peak current can achieve complete material vaporization and removal, resulting in a machined surface without a recast layer. A combination of longer pulse widths and appropriate peak currents can balance machining efficiency and tool electrode wear. However, under a fixed peak current, excessively long pulse widths can lead to a stable electric field distribution, solidified discharge channels, and multiple pulses concentrating in the same channel, causing arcing and carbon buildup, which can severely damage the tool electrode and workpiece. To avoid this problem, current technologies typically employ a conservative combination of pulse width and peak current. While this improves machining safety, it significantly reduces machining efficiency and still cannot completely prevent pinhole defects caused by abnormal discharges.

[0004] Furthermore, the discharge gap is smaller and chip removal conditions are worse in the intermediate finishing stage, making it highly susceptible to arcing and carbon buildup. Simultaneously, this stage has the longest processing cycle, and operators often extend the pulse width to pursue efficiency, further exacerbating the risk of abnormal discharge. More critically, the peak current in intermediate finishing is relatively small, and the difference in current characteristics between normal and abnormal discharges is minimal, requiring extremely high detection sensitivity. Traditional Hall effect sensors, under the strong electromagnetic interference of electrical spark discharges, struggle to meet the high-precision detection requirements for small currents (0.1A–7.9A), resulting in low accuracy in abnormal discharge detection and severely impacting mold processing quality and efficiency.

[0005] Therefore, there is an urgent need for an abnormal discharge current detection solution that is suitable for medium-precision machining scenarios, has strong anti-interference capabilities, and high detection sensitivity, in order to solve the technical problems of difficulty in balancing processing efficiency and surface quality and insufficient detection accuracy in existing technologies. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method and device for detecting abnormal discharge current in electrical discharge machining, so as to solve the problems in the prior art where the discharge gap is small during medium and fine machining, making it difficult to remove machining chips, easily causing abnormal discharge, and the discharge current is small, and Hall sensors are difficult to use in strong electromagnetic interference environments.

[0007] According to a first aspect of the present invention, a method for detecting abnormal discharge current in electrical discharge machining is provided, the method comprising:

[0008] Obtain the target processing stage of electrical discharge machining and the corresponding range of discharge parameters; A current detection branch is constructed based on a DC-DC power supply module. The current detection branch is connected in series with a current limiting resistor, an isolation diode and a controlled switch, and then connected between the positive and negative terminals of the pulse discharge power supply for electrical discharge processing. After the discharge gap breaks down, a timing is triggered and the detection voltage values ​​at the first preset time point and the second preset time point are obtained respectively. The detection voltage values ​​are generated by the DC-DC power supply module in response to the current change of the discharge gap. Retrieve two comparison reference values ​​corresponding to the current peak current from the preset reference value lookup table, namely the first reference value and the second reference value; The detected voltage value at the first preset time point is compared with the first reference value, and the detected voltage value at the second preset time point is compared with the second reference value. If the detection voltage value at the first preset time point is greater than the first reference value, or the detection voltage value at the second preset time point is less than the second reference value, then it is determined to be an abnormal discharge state.

[0009] Preferably, The preset benchmark lookup table includes: For different peak current levels, discharge experiments were conducted under the target processing scenario, and voltage data were collected at the two preset time points corresponding to normal discharge and abnormal discharge respectively. Based on the voltage data, a first reference value and a second reference value are calibrated for each peak current level to form a reference value lookup table.

[0010] Preferably, The conduction state of the controlled switch is controlled by the power switch gate signal of the pulse discharge power supply, and the gate signal is taken from the discharge control system of the pulse discharge power supply.

[0011] Preferably, The trigger signals for timing at the first and second preset time points are discharge voltage breakdown edge detection signals. The detection signals are taken from the discharge control system of the pulse discharge power supply and the signal acquisition at the two preset time points is controlled by a monostable trigger.

[0012] Preferably, The isolation diode is a fast recovery diode. When the voltage after the discharge gap breaks down is lower than the output voltage of the DC-DC power supply module, the fast recovery diode is forward-biased, and the current detection branch is connected to the discharge circuit.

[0013] Preferably, it further includes: The parameters for the target processing scenario are set, including: the type of electrical discharge machining fluid, the workpiece material, and the electrode material; The discharge processing fluid is one of kerosene-based, deionized water, or a mixture of emulsion and tap water. The workpiece material is SKD11 steel, and the electrode material is copper.

[0014] According to a second aspect of the present invention, an abnormal discharge current detection device for electrical discharge machining is provided, the device being applied to the method described in any one of the above embodiments, the device comprising, A DC-DC power supply module is used to generate a detection voltage signal in response to the current change in the discharge gap. The positive and negative input terminals of the DC-DC power supply module are connected to the standard power supply and the common ground, respectively. The positive output terminal of the DC-DC power supply module is connected to the positive terminal of the isolation diode D1, and the negative output terminal is connected to the negative output terminal of the pulse discharge power supply. The isolation current limiting unit includes: an isolation diode D1, a first current limiting resistor R1, and a second current limiting resistor R2. The positive terminal of the isolation diode D1 is connected to the positive output terminal of the DC-DC power supply module, and the negative terminal of the isolation diode D1 is connected in series with the first current limiting resistor R1 and then connected to the source S of the controlled switch T1. The drain D of the controlled switch T1 is connected in series with the second current limiting resistor R2 and then connected to the positive output terminal of the pulse discharge power supply. The switch control unit includes an optocoupler and a third resistor R3. The positive terminal of the light-emitting diode of the optocoupler is connected to one end of the resistor R10, and the other end of the resistor R10 is connected to the positive terminal of the detection gate signal. The negative terminal of the light-emitting diode of the optocoupler is connected to the negative terminal of the detection gate signal, which is taken from the discharge control system of the pulse discharge power supply. The emitter of the output transistor of the optocoupler is connected to the gate G of the controlled switch T1 through the third resistor R3, and the collector of the output transistor of the optocoupler is connected to a standard power supply through the resistor R20, for controlling the conduction and cutoff of the controlled switch T1. The signal acquisition and comparison unit includes a first comparator, a second comparator, a first D / A converter, and a second D / A converter. The drain D of the controlled switch T1 serves as the detection output terminal, and is connected in series with resistors R4 and R6 to the negative terminal of the first comparator and the positive terminal of the second comparator, respectively. The positive terminal of the first comparator is connected to one end of resistor R5, and the other end of resistor R5 is connected to the output terminal of the first D / A converter. The input terminal of the first D / A converter is connected to a digital signal of a first reference value. The negative terminal of the second comparator is connected to one end of resistor R7, and the other end of resistor R7 is connected to the output terminal of the second D / A converter. The input terminal of the second D / A converter is connected to a digital signal of a second reference value. A timing control unit includes a first monostable multivibrator, a second monostable multivibrator, a first AND gate, and a second AND gate. The first input of the first AND gate is connected to the output of the first comparator. The second input of the first AND gate is connected to the output of the first monostable multivibrator. The output pulse width of the first monostable multivibrator is determined by capacitor C3, resistor R14, and adjustable resistor R13, and the pulse width is adjusted to a first preset time point. The input of the first monostable multivibrator is connected to a discharge voltage breakdown edge detection signal. The first input of the second AND gate is connected to the output of the second comparator. The second input of the second AND gate is connected to the output of the second monostable multivibrator. The output pulse width of the second monostable multivibrator is determined by capacitor C2, resistor R12, and adjustable resistor R11, and the pulse width is adjusted to a second preset time point. The input of the second monostable multivibrator is connected to a discharge voltage breakdown edge detection signal. The signal output unit has the output terminals of the first AND gate and the second AND gate used to output the abnormal discharge determination result, which is used to feed back to the discharge control system of the pulse discharge power supply.

[0015] Preferably, The output pulse width of the first monostable multivibrator is 5 μs, and the output pulse width of the second monostable multivibrator is 15 μs.

[0016] Preferably, The first and second comparators are constructed from general-purpose operational amplifiers, and the outputs of both the first and second comparators are connected to the standard power supply via pull-up resistors.

[0017] Preferably, The voltage difference between the positive and negative output terminals of the DC-DC power supply module is the highest discharge voltage value after the discharge gap breaks down.

[0018] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects: This application uses a DC-DC power supply module as the core component for current detection. It has stable voltage output characteristics and is sensitive to current fluctuations, replacing traditional Hall sensors and successfully solving the problem of high-precision detection of small currents in environments with strong electromagnetic interference. Based on the difference in current rise edge characteristics between abnormal discharge and normal discharge, two key time points, the first and second preset time points, are selected for voltage comparison. This can accurately distinguish abnormal states such as excessive arc, arc, short circuit (steep rise edge), and micro-open circuit (gentle rise edge), avoiding missed detections and false detections. Through experimental calibration, a reference value lookup table corresponding to different peak currents is established, enabling adaptive reference value retrieval without manual adjustment, adapting to various medium and fine machining parameter scenarios. The detection branch adopts an isolation diode and current-limiting resistor design, combined with pulsed intermittent measurement of the controlled switching transistor, to avoid shunt interference to the main discharge circuit and ensure the stability of the machining process.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0021] Figure 1 This is a flowchart illustrating an abnormal discharge current detection method for electrical discharge machining according to an exemplary embodiment. Figure 2 This is a schematic diagram illustrating the characteristics of various abnormal discharge states during intermediate finishing, according to another exemplary embodiment; Figure 3 This is a schematic diagram of the circuit principle of an abnormal discharge current detection device for electrical discharge machining according to another exemplary embodiment. Detailed Implementation

[0022] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0023] Example 1 Figure 1 This is a flowchart illustrating an abnormal discharge current detection method for electrical discharge machining according to an exemplary embodiment, such as... Figure 1 As shown, the method includes: S1, Obtain the target processing stage of electrical discharge machining and the corresponding range of discharge parameters; S2, a current detection branch is constructed based on the DC-DC power supply module. The current detection branch is connected in series with a current limiting resistor, an isolation diode and a controlled switch, and then connected between the positive and negative terminals of the pulse discharge power supply for discharge processing. S3, after the discharge gap breaks down, a timing is triggered and the detection voltage values ​​at the first preset time point and the second preset time point are obtained respectively. The detection voltage values ​​are generated by the DC-DC power supply module in response to the current change of the discharge gap. S4. Obtain two comparison reference values ​​corresponding to the current peak current from the preset reference value lookup table, namely the first reference value and the second reference value. S5, compare the detection voltage value corresponding to the first preset time point with the first reference value, and compare the detection voltage value corresponding to the second preset time point with the second reference value; S6. If the detection voltage value corresponding to the first preset time point is greater than the first reference value, or the detection voltage value corresponding to the second preset time point is less than the second reference value, then it is determined to be an abnormal discharge state. It is understood that, for ease of understanding of this application, the following design principles are presented in this embodiment: According to the theory of electrical discharge machining (EDM), there are five discharge states in EDM: open circuit, normal discharge, excessive arc, arc, and short circuit. For EDM with low surface finish requirements, excessive arc is acceptable and can improve processing efficiency. However, in EDM for integrated circuit packaging molds, the requirements for consistent mold surface roughness are stringent, and pinhole-like defects are unacceptable. Therefore, in this type of EDM, excessive arc, arc, and short circuit must all be classified as abnormal discharge states, which places higher demands on detection. In rough EDM, due to the large discharge gap, high discharge current, and good chip removal conditions, the probability of arcing and short circuits is much lower. However, in medium and finish EDM, the small discharge gap and poor chip removal conditions easily lead to abnormal discharges.

[0024] Characteristic identification of abnormal discharge states, as shown in the appendix. Figure 2As shown, curve a represents the arc discharge state, with a steep rising edge of the current waveform, high current value, and smooth waveform; curve b represents the excessive arc discharge state, with a relatively steep rising edge of the current waveform and low-frequency fluctuations in the waveform; curve c represents the normal spark discharge state, with a relatively gentle rising edge of the current waveform and high-frequency fluctuations in the waveform; curve d represents the micro-open circuit discharge state, with an extremely gentle rising edge of the current waveform and a very small current value. Based on the current waveform characteristics of the above discharge states, this invention proposes to detect the rising edge of the discharge pulse current under combined discharge conditions of a current pulse width greater than 30 μs and a peak current less than 8 amperes. Based on the waveform characteristics of abnormal discharge, the current values ​​at 5 μs and 15 μs are compared. An abnormal discharge state is determined if the current value is greater than the set standard value at 5 μs or less than the set standard value at 15 μs. The first and second reference values ​​are set according to different peak currents. Based on the power supply parameters of commonly used EDM machines, the minimum peak current is 0.1A, which places high demands on the sensitivity of the detection. General Hall effect sensors are insufficient, especially under the strong electromagnetic interference of EDM discharge. Therefore, this embodiment proposes using a DC-DC power supply module as a small current sensor. The DC-DC power supply module can provide a stable voltage and is sensitive to fluctuations in the output current. This application utilizes this characteristic to overcome the aforementioned difficulties. The positive and negative terminals of the discharge pulse power supply to be detected are connected to the output terminal of the DC-DC power supply module and connected in series with a current-limiting resistor and a control switch. Because the power supply module is small, it cannot perform long-term measurements; therefore, the switch is required for intermittent pulse measurements. To prevent the measurement branch from shunting the small current in the discharge circuit, this application proposes using a DC-DC power supply module for measurement. The voltage change at the output terminal of the discharge power supply is used to excite the DC-DC power supply module to generate a corresponding rapidly responding changing current, thereby mapping the current change in the discharge gap. Specific details include: As attached Figure 3As shown, the Vin and -Vin pins of the DC-DC power conversion module are connected to the standard power supply Vcc (e.g., +5V) and common ground, respectively. The -Vout pin of the DC-DC power conversion module is connected to the detection point, i.e., the negative output terminal of the pulse discharge power supply. The +Vout pin of the DC-DC power conversion module is connected to the positive terminal of the isolation diode D1. The negative terminal of the isolation diode D1 is connected to resistor R1. The other end of resistor R1 is connected to the source S of the controlled switch T1. The drain D of the controlled switch T1 is connected to resistor R2. The other end of resistor R2 is connected to the other end of the detection point, i.e., the positive output terminal of the pulse discharge power supply. Thus, after the discharge gap breaks down, a very small portion of the discharge current returns to the negative output terminal of the pulse discharge power supply through resistor R2, the controlled switch T1, resistor R1, isolation diode D1, and the DC-DC power conversion module. The larger the values ​​of resistors R1 and R2, the smaller the current drawn from the power supply, and the smaller the impact on the discharge processing current. Of course, this also requires a higher sensitivity from the DC-DC power conversion module.

[0025] The difference between -Vout and +Vout is the highest voltage value after the discharge gap breaks down.

[0026] When the discharge gap breaks down, the voltage between the positive and negative output terminals of the pulse discharge power supply will be lower than the voltage between -Vout and +Vout. This will cause the isolation diode D1 to conduct in the forward direction, which also determines that the controlled switch T1 is in the conducting state.

[0027] The gate G of the controlled switch T1 is connected to resistor R3. The other end of resistor R3 is connected to the emitter of the output transistor of the optocoupler. The collector of the output transistor of the optocoupler is connected to the standard voltage Vcc through resistor R20. The positive terminal of the LED of the optocoupler is connected to resistor R10. The other end of resistor R10 is connected to the positive terminal of the detection gate signal. The negative terminal of the LED of the optocoupler is connected to the negative terminal of the detection gate signal. The detection gate signal is taken from the gate signal of the power switch of the discharge pulse power supply.

[0028] The drain D terminal of the controlled switch T1 is connected to resistors R4 and R6 as the detection output terminal. The other end of resistor R4 is connected to the negative terminal of the first comparator, and the other end of resistor R6 is connected to the positive terminal of the second comparator.

[0029] The first and second comparators are constructed from general-purpose operational amplifiers.

[0030] The positive terminal of the first comparator is connected to resistor R5, and the other end of resistor R5 is connected to the output terminal of the first D / A digital-to-analog converter; the negative terminal of the second comparator is connected to resistor R7, and the other end of resistor R7 is connected to the output terminal of the second D / A digital-to-analog converter.

[0031] The input terminal of the first D / A digital-to-analog converter is the digital signal input value—the first reference value UD1-UD8 at the first preset time point; the input terminal of the second D / A digital-to-analog converter is the digital signal input value—the second reference value DD1-DD8 at the second preset time point.

[0032] If the voltage at the drain D point of the controlled switch T1 is higher than the first reference value at the first preset time point, the first comparator outputs a high value, indicating an abnormal discharge; if the voltage at the drain D point of the controlled switch T1 is lower than the second reference value at the second preset time point, the second comparator outputs a high value, also indicating an abnormal discharge.

[0033] The outputs of the first and second comparators are time-controlled (5μs, 15μs). The output of the first comparator is connected to the standard power supply Vcc via pull-up resistor R8. The output of the first comparator is also connected to the first input of the first AND gate. The second input of the first AND gate is connected to the output of the first monostable multivibrator (MSF). The output pulse width of the first MSF is determined by capacitor C3, resistor R14, and adjustable resistor R13, and is adjusted to 5μs. The input of the first MSF is connected to the discharge voltage breakdown edge detection signal (provided by the discharge control system of the pulse power supply and triggering the timing). The output of the second comparator is connected to the standard power supply Vcc via pull-up resistor R9. The output of the second comparator is also connected to the first input of the second AND gate. The second input of the second AND gate is connected to the output of the second MSF. The output pulse width of the second MSF is determined by capacitor C2, resistor R12, and adjustable resistor R11. The input of the second MSF is connected to the discharge voltage breakdown edge detection signal (provided by the discharge control system of the pulse power supply and triggering the timing). The first reference values ​​UD1-UD8 and the second reference values ​​DD1-DD8 can be obtained from actual measurements of pulse peak currents ranging from 0.1 to 7.9 amperes in discharge machining experiments and set into a table stored in a read-only memory or microcontroller. The detection device proposed in this application needs to be installed on the discharge control system of the pulse power supply, requires the use of the gate signal of the discharge control system, and simultaneously controls the discharge control system based on the output signal of this device.

[0034] Example 2: This embodiment provides the process for determining the first and second benchmark values ​​mentioned above, specifically including: To determine the first reference value for the first preset time point (5μs) and the second reference value for the second preset time point (15μs), this embodiment conducted an actual calibration experiment on an EDM machine. The experiment used kerosene-based working fluid, SKD11 steel as the workpiece, and copper as the electrode. Since the rising slope of the normal discharge waveform differs under different peak currents, threshold values ​​need to be set for different current levels. The following are data from two typical embodiments. Case 1: Processing conditions with peak current Ip = 2.0A; Under this current condition, observation with an oscilloscope and circuit sampling revealed the following: Arc / Short Circuit (Abnormally Steep): At 5μs, the voltage at the detection point (T1 drain) is typically higher than 3.5V.

[0035] Normal discharge (moderate slope): The voltage is approximately 2.0 to 3.0V at 5μs; the voltage accumulates to over 3.5V at 15μs.

[0036] Micro-open circuit (abnormally smooth): At 15μs, the voltage at the detection point is still below 1.5V.

[0037] Therefore, the reference value for this current range is set as follows: The first reference value at the first preset time point is set to 3.2V. If the detected value is greater than 3.2V, it is determined to be an arc / short circuit.

[0038] The second reference value at the second preset time point is set to 2.5V. If the detected value is less than 2.5V, it is determined to be a micro-open circuit.

[0039] Example 2: Ultra-precision machining conditions with peak current Ip = 0.5A; Under this low current condition, the discharge energy is weak, the overall waveform rises at a slower rate, and the voltage amplitude response is correspondingly reduced.

[0040] Arc / Short Circuit: At 5μs, the voltage at the detection point is typically around 2.5V.

[0041] Normal discharge: The voltage is approximately 1.2 to 1.8V at 5μs; the voltage accumulates to over 2.0V at 15μs.

[0042] Micro-open circuit: At 15μs, the voltage at the detection point is still below 1.0V.

[0043] Continuing to use the high threshold from Case 1 will lead to misjudgment (misjudging normal discharge as a micro-open circuit), therefore the baseline value needs to be adjusted: The first baseline value at the first preset time point is set to 2.0V.

[0044] The second reference value at the second preset time point is lowered and set to 1.2V.

[0045] Based on the above method, the peak current was measured for each range from 0.1 to 7.9A, and the resulting lookup table was stored in the microcontroller:

[0046] When the control system is running, it reads the currently set peak current value, looks up the corresponding first reference value and second reference value in the table, and inputs them into the first D / A converter and the second D / A converter, thereby realizing adaptive and accurate detection of abnormal discharge.

[0047] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0048] It should be noted that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means at least two.

[0049] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0050] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0051] Those skilled in the art will understand that all or part of the steps of the methods described in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it includes one or a combination of the steps of the method embodiments.

[0052] Furthermore, the functional units in the various embodiments of the present invention can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0053] The storage media mentioned above can be read-only memory, disk, or optical disk, etc.

[0054] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0055] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for detecting abnormal discharge current in electrical discharge machining, characterized in that, The method includes: Obtain the target processing stage of electrical discharge machining and the corresponding range of discharge parameters; A current detection branch is constructed based on a DC-DC power supply module. The current detection branch is connected in series with a current limiting resistor, an isolation diode and a controlled switch, and then connected between the positive and negative terminals of the pulse discharge power supply for electrical discharge processing. After the discharge gap breaks down, a timing is triggered and the detection voltage values ​​at the first preset time point and the second preset time point are obtained respectively. The detection voltage values ​​are generated by the DC-DC power supply module in response to the current change of the discharge gap. Retrieve two comparison reference values ​​corresponding to the current peak current from the preset reference value lookup table, namely the first reference value and the second reference value; The detected voltage value at the first preset time point is compared with the first reference value, and the detected voltage value at the second preset time point is compared with the second reference value. If the detection voltage value at the first preset time point is greater than the first reference value, or the detection voltage value at the second preset time point is less than the second reference value, then it is determined to be an abnormal discharge state.

2. The method according to claim 1, characterized in that, The preset benchmark lookup table includes: For different peak current levels, discharge experiments were conducted under the target processing scenario, and voltage data were collected at the two preset time points corresponding to normal discharge and abnormal discharge respectively. Based on the voltage data, a first reference value and a second reference value are calibrated for each peak current level to form a reference value lookup table.

3. The method according to claim 2, characterized in that, The conduction state of the controlled switch is controlled by the power switch gate signal of the pulse discharge power supply, and the gate signal is taken from the discharge control system of the pulse discharge power supply.

4. The method according to claim 3, characterized in that, The trigger signals for timing at the first and second preset time points are discharge voltage breakdown edge detection signals. The detection signals are taken from the discharge control system of the pulse discharge power supply and the signal acquisition at the two preset time points is controlled by a monostable trigger.

5. The method according to claim 4, characterized in that, The isolation diode is a fast recovery diode. When the voltage after the discharge gap breaks down is lower than the output voltage of the DC-DC power supply module, the fast recovery diode is forward-biased, and the current detection branch is connected to the discharge circuit.

6. The method according to claim 5, characterized in that, Also includes: The parameters for the target processing scenario are set, including: the type of electrical discharge machining fluid, the workpiece material, and the electrode material; The discharge processing fluid is one of kerosene-based, deionized water, or a mixture of emulsion and tap water. The workpiece material is SKD11 steel, and the electrode material is copper.

7. A device for detecting abnormal discharge current in electrical discharge machining, characterized in that, The apparatus is used in the method according to any one of claims 1-6, and the apparatus comprises: A DC-DC power supply module is used to generate a detection voltage signal in response to the current change in the discharge gap. The positive and negative input terminals of the DC-DC power supply module are connected to the standard power supply and the common ground, respectively. The positive output terminal of the DC-DC power supply module is connected to the positive terminal of the isolation diode D1, and the negative output terminal is connected to the negative output terminal of the pulse discharge power supply. The isolation current limiting unit includes: an isolation diode D1, a first current limiting resistor R1, and a second current limiting resistor R2. The positive terminal of the isolation diode D1 is connected to the positive output terminal of the DC-DC power supply module, and the negative terminal of the isolation diode D1 is connected in series with the first current limiting resistor R1 and then connected to the source S of the controlled switch T1. The drain D of the controlled switch T1 is connected in series with the second current limiting resistor R2 and then connected to the positive output terminal of the pulse discharge power supply. The switch control unit includes an optocoupler and a third resistor R3. The positive terminal of the light-emitting diode of the optocoupler is connected to one end of the resistor R10, and the other end of the resistor R10 is connected to the positive terminal of the detection gate signal. The negative terminal of the light-emitting diode of the optocoupler is connected to the negative terminal of the detection gate signal, which is taken from the discharge control system of the pulse discharge power supply. The emitter of the output transistor of the optocoupler is connected to the gate G of the controlled switch T1 through the third resistor R3, and the collector of the output transistor of the optocoupler is connected to a standard power supply through the resistor R20, for controlling the conduction and cutoff of the controlled switch T1. The signal acquisition and comparison unit includes a first comparator, a second comparator, a first D / A converter, and a second D / A converter. The drain D of the controlled switch T1 serves as the detection output terminal, and is connected in series with resistors R4 and R6 to the negative terminal of the first comparator and the positive terminal of the second comparator, respectively. The positive terminal of the first comparator is connected to one end of resistor R5, and the other end of resistor R5 is connected to the output terminal of the first D / A converter. The input terminal of the first D / A converter is connected to a digital signal of a first reference value. The negative terminal of the second comparator is connected to one end of resistor R7, and the other end of resistor R7 is connected to the output terminal of the second D / A converter. The input terminal of the second D / A converter is connected to a digital signal of a second reference value. A timing control unit includes a first monostable multivibrator, a second monostable multivibrator, a first AND gate, and a second AND gate. The first input of the first AND gate is connected to the output of the first comparator. The second input of the first AND gate is connected to the output of the first monostable multivibrator. The output pulse width of the first monostable multivibrator is determined by capacitor C3, resistor R14, and adjustable resistor R13, and the pulse width is adjusted to a first preset time point. The input of the first monostable multivibrator is connected to a discharge voltage breakdown edge detection signal. The first input of the second AND gate is connected to the output of the second comparator. The second input of the second AND gate is connected to the output of the second monostable multivibrator. The output pulse width of the second monostable multivibrator is determined by capacitor C2, resistor R12, and adjustable resistor R11, and the pulse width is adjusted to a second preset time point. The input of the second monostable multivibrator is connected to a discharge voltage breakdown edge detection signal. The signal output unit has the output terminals of the first AND gate and the second AND gate used to output the abnormal discharge determination result, which is used to feed back to the discharge control system of the pulse discharge power supply.

8. The apparatus according to claim 7, characterized in that, The output pulse width of the first monostable multivibrator is 5 μs, and the output pulse width of the second monostable multivibrator is 15 μs.

9. The apparatus according to claim 8, characterized in that, The first and second comparators are constructed from general-purpose operational amplifiers, and the outputs of both the first and second comparators are connected to the standard power supply via pull-up resistors.

10. The apparatus according to claim 9, characterized in that, The voltage difference between the positive and negative output terminals of the DC-DC power supply module is the highest discharge voltage value after the discharge gap breaks down.

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